In this chapter, we will discuss the various types
of indicators in use today. These indicators range
from the heading indicators to the newest heads-up
display (HUD) tactical displays. Every effort was
made to include as many different platforms as
Identify the types of
heading indicators and their primary
The two heading indicators that we will be
discussing are the horizontal situation indicator (HSI)
and the bearing-distance-heading indicator (BDHI).
Both of these indicators are used on many different
types of aircraft. The information displayed by these
indicators comes from the various navigational
systems on the aircraft. The HSI displays more
information than the BDHI.
HORIZONTAL SITUATION INDICATOR
The HSI system we will discuss is the system in
use on the P3-C aircraft. The HSI group provides the
pilot, copilot, and NAV/COMM operator with a visual
display of aircraft course, bearing, heading, and
distance to a selected point.
The HSI group consists of three ID-1540/A
indicators and three control boxes. The three control
boxes are the pilots control, copilots control, and the
NAV/COMMs control. The three ID-1540/As are
interchangeable between the three stations, but the
control boxes are not.
ID-1540/A HORIZONTAL SITUATION
INDICATOR. The ID-1540/A indicator (fig. 5-1) is
a multipurpose aircraft situation indicator. It keeps
the pilot, copilot, and the NAV/COMM operator
informed of the aircrafts situation at any given
Refer to figure 5-1 while reading the
1. The lubber line is the reference line for
reading the aircrafts heading on the compass card.
2. Bearing pointer 1 points to the bearing of the
selected navigational point.
3. The heading marker indicates the desired
heading as set by the HEADING SET knob.
4. The course arrow indicates the course set by
the COURSE SET knob in the radio navigation mode.
This arrow indicates the course set by the computer in
the tactical navigational mode.
5. The COURSE indicator displays, in degrees,
a digital readout of the course arrow setting.
6. The mode lights indicate the operating mode
selected on the HSI control box for that station.
7. The course deviation bar indicates deviation
relative to the course arrow position for VOR or
Figure 5-1.-ID-1540/A horizontal situation indicator.